Chapter 8 High-Level Programming Languages

8-2 Chapter Goals Describe the translation process and distinguish between assembly, compilation, interpretation, and execution Name four distinct programming paradigms and name a language characteristic of each Describe the following 4 constructs: sequential, selection (branching), looping, and subprograms Construct Boolean expressions and describe how they are used to alter the flow of control of an algorithm

8-3 Chapter Goals Define the concepts of a data type Explain the concept of a parameter

8-4 Compilers Compiler A program that translates a high-level language program into machine code High-level languages provide a richer set of instructions that makes the programmer’s life even easier

8-5 Compilers Figure 8.1 Compilation process

8-6 Interpreters Interpreter A translating program that translates and executes the statements in sequence –Unlike an assembler or compiler which produce machine code as output, which is then executed in a separate step –An interpreter translates a statement and then immediately executes the statement –Interpreters can be viewed as simulators

8-7 Java Introduced in 1996 and swept the computing community by storm Portability was of primary importance Java is compiled into a standard machine language called Bytecode A software interpreter called the JVM (Java Virtual Machine) takes the Bytecode program and executes it

8-8 Programming Language Paradigms What is a paradigm? A set of assumptions, concepts, values, and practices that constitute a way of viewing reality

8-9 Programming Language Paradigms Figure 8.2 Portability provided by standardized languages versus interpretation by Bytecode

8-10 Programming Language Paradigms Figure 8.2 Portability provided by standardized languages versus interpretation by Bytecode

8-11 Programming Language Paradigms Imperative or procedural –FORTRAN, COBOL, BASIC, C Functional model –LISP Logic programming –PROLOG Object-oriented –C++, Java

8-12 Structures in Algorithms or Programming Languages Sequence Executing statements in sequence until an instruction is encountered that changes this sequencing Selection Deciding which action to take Iteration (looping) Repeating an action Subprogram (Both selection and iteration require the use of a Boolean expression)

8-13 Boolean Expressions Boolean expression A sequence of identifiers, separated by compatible operators, that evaluates to true or false Boolean expression can be –A Boolean variable –An arithmetic expression followed by a relational operator followed by an arithmetic expression

8-14 Boolean Expressions Variable A location in memory that is referenced by an identifier that contains a data value Thus, a Boolean variable is a location in memory that can contain either true or false

8-15 Boolean Expressions A relational operator between two arithmetic expressions is asking if the relationship exists between the two expressions For example, xValue < yValue Page 233

8-16 Data Types Data type A description of the set of values and the basic set of operations that can be applied to values of the type

8-17 Some Data Types Integer numbers Real numbers Characters Boolean values Strings

8-18 Integers The range varies depending upon how many bytes are assigned to represent an integer value Some high-level languages provide several integer types of different sizes Use standard arithmetic and relational operations Usually stored in 2’s-complement form

8-19 Reals Like the integer data type, the range varies depending on the number of bytes assigned to represent a real number Many high-level languages have two sizes of real numbers The operations that can be applied to real numbers are the same as those that can be applied to integer numbers

8-20 Characters It takes one byte to represent characters in the ASCII character set Two bytes to represent characters in the Unicode character set Our English alphabet is represented in ASCII, which is a subset of Unicode

8-21 Characters Applying arithmetic operations to characters doesn’t make much sense Comparing characters does make sense, so the relational operators can be applied to characters The meaning of “less than” and “greater than” when applied to characters is “comes before” and “comes after” in the character set

8-22 Boolean The Boolean data type consists of two values: true and false

8-23 Strings A string is a sequence of characters considered as one data value For example: “This is a string.” –Containing 17 characters: one uppercase letter, 12 lowercase letters, three blanks, and a period The operations defined on strings vary from language to language –They include concatenation of strings and comparison of strings in terms of lexicographic order

8-24 Declarations Declaration A statement that associates an identifier with a variable, an action, or some other entity within the language that can be given a name so that the programmer can refer to that item by name

Declarations 8-26 In original BASIC this is not required. Variables that have a $ are strings, others are real. In languages like Java, one has to declare a variable’s type at the beginning of a program (strong typing)

8-26 Declarations Reserved word A word in a language that has special meaning Case-sensitive Uppercase and lowercase letters are considered the same

8-27 Assignment statement Assignment statement An action statement (not an equation) that says to evaluate the expression on the right-hand side of the symbol and store that value into the place named on the left-hand side Named constant A location in memory, referenced by an identifier, that contains a data value that cannot be changed

Assignment Statement Page In original BASIC 10 LET X = 2

8-29 Input/Output Structures In our pseudocode algorithms we have used the expressions Read and Write High-level languages view input data as a stream of characters divided into lines

8-30 Input/Output Structures We do not give examples of input/output statements because the syntax is often quite complex and differs so widely among high-level languages In original BASIC it’s not so tough: 20 PRINT X 30 PRINT “HELLO” 40 PRINT “X = “, X

8-31 Control Structures Control structure An instruction that determines the order in which other instructions in a program are executed Sequence, selection statements, looping statements, and subprogram statements are control structures

8-32 Selection (Branch) Statements Figure 8.3 Flow of control of if statement

8-33 Selection Statements The if statement allows the program to test the state of the program variables using a Boolean expression In original BASIC 20 IF T < 75 THEN PRINT “No jacket is necessary” 40 GOTO PRINT “A light jacket is appropriate” 60 END

8-34 Looping Statements The while statement is used to repeat a course of action Let’s look at two distinct types of repetitions

8-35 Looping Statements Count-controlled loops –Repeat a specified number of times –Use of a special variable called a loop control variable Figure 8.4 Flow of control of while statement

8-36 Looping Statements Count-controlled loops In original BASIC 10 FOR N = 1 to PRINT “HELLO” 30 NEXT N

8-37 Subprogram Statements We can give a section of code a name and use that name as a statement in another part of the program When the name is encountered, the processing in the other part of the program halts while the named code is executed

8-38 Subprogram Statements There are times when the calling unit needs to give information to the subprogram to use in its processing A parameter list is a list of the identifiers with which the subprogram is to work, along with the types of each identifier placed in parentheses beside the subprogram name

8-39 Subprogram Statements Figure 8.5 Subprogram flow of control

8-40 Subprogram Statements Figure 8.5 Subprogram flow of control

8-41 Subprogram Statements In original BASIC 10 GOSUB PRINT “Subroutine returns here 30 GOTO PRINT “Printed within subprogram” 50 RETURN 60 END